1. Field of the Invention
The present invention relates to a magnetic disk memory which comprises a hub rotatably mounted at both ends in a one-piece supporting shell of a housing, carrying at least one storage disk and driven by a drive motor, the hub being fixed on a rotating spindle, whereby a pair of ball bearings is provided for rotatably seating the spindle at mutually opposite walls of the supporting shell, the ball bearings being braced in the axial direction in order to achieve a play-free spindle guidance.
2. Description of the Prior Art
A distinction is generally made in magnetic disk memories between memories having fixed disk packs and exchangeable disk packs. Technical develpment is continuing to proceed in the direction of higher and higher storage capacities both in view of the track density and bit density as the characteristic for the storage capacity per disk face, on the one hand, and in view of the mechanical structure in order to be able to accommodate as many magnetic disks as possible in a prescribed mounting space. As an example of this is the so-called 51/4" inch fixed disk memory whose magnetic disk have an outer diameter of 130 mm and an inner diameter of 40 mm according to the German industrial standard. Analogous to the dimensions of the competing floppy disk drives, a mounting space having a mounting height of 82.5 mm and a base area of 146mm.times.203 mm has crystallized for this type of memory as a uniform size which is available for the overall apparatus including the housing and the appertaining electronics.
The desire to accommodate as many magnetic disks as possible in this prescribed mounting space is subordinate to the developmental goal of higher storage capacities and to the efforts to increase the recording density on the magnetic disks themselves. Within the scope of this structural endeavor, embodiments of the 51/4" fixed disk memories have been disclosed in which the drive motor for the disk pack has been miniaturized to such a degree and has been structurally designed such that it can still be built into the hub of the disk pack, even given a prescribed inner diameter of 40 mm for the disk packs. An element which has a significant co-determining effect on the overall height of conventional fixed disk memories is therefore integrated in the hub of the magnetic disk pack and the overall height exploitable for the disk pack is thus expanded. Based on current conditions in the size of the combined magnetic heads and of the disk thickness, disk packs which contain up to eight magnetic disks stacked on top of one another have thus become possible. The remaining overall height is required for the housing and for the device electronics.
As mentioned above, the recording density on the magnetic disk is the product of the write density times the track density. A significant criterion for the structaral format of the magnetic disk memory also derives for the case of the present invention specifically from track density having, for example, more than 1000 tracks per inch. This high track density requires a best possible vibration-free seating of the spindle of the disk pack in the housing. Requirements are therefore made for this type of memory such as heretofore played a part only with large disk memories, for example the 14" disk memories.
With respect to conventional large disk memories, it is generally known to seat the spindle of the disk pack at one end in a heavy base plate, employing highly sophisticated structures, this particularly applying to interchangeable disk memories in disk memories designed to utilize replaceable disk packs. Structures are also known in which the spindle is mounted at both ends in a rigid housing surrounding the disk pack. In order to achieve as vibration-free a spindle seating as possible, a fixed bearing and a movable bearing are employed with this two-sided seating and a spring is provided adjacent the movable bearing, the spring tensing the two bearings relative to one another after assembly such that a coaxial spindle guidance that is as free of play as possible is achieved. In practice, this goal, however, can only be achieved to a limited extent. Furthermore, additional mounting space is required for the incorporation of the spring, this therefore being lost as useable storage space.